In order to handle increasing demands for high data rate communications, fiber optic databus systems require the ability to multiplex wavelengths. Wavelength division multiplexing (WDM) is considered to be a promising technique to enhance the transmission capacity of an optical fiber communication system. The range in which wavelengths can be multiplexed, is limited by the luminescence spectrum of semiconductor diode lasers, which has a useful bandwidth of only 200 to 300 .ANG.. In order to propagate the greatest number of channels within this narrow spectrum, the wavelengths must be very stable and tightly controlled.
The best wavelength stabilized diode lasers available today are the distributed feedback laser (DFB) and the distributed Bragg reflector laser (DBR). The range of operating temperatures over which all diode lasers are normally operated is about 20.degree. C. to 70.degree. C. The variation in wavelength is about 5 .ANG./.degree.C. for laser diodes with conventional cavities, and about 1 .ANG./.degree.C. for DFB or DBR lasers. Therefore, the wavelength will drift about 50 .ANG. over the required temperature range for even the best stabilized lasers, using up to 1/4 of the entire useful bandwidth for only one channel.
Lasers which incorporate Bragg reflectors are subject to wavelength variations due to changes in refractive index, according to the relationship .lambda..sub.peak =2.LAMBDA.n.sub.eff, where .lambda..sub.peak is the peak wavelength of the grating, .LAMBDA. is the spacing of the grating and n.sub.eff is the effective refractive index of the waveguide in which the grating is formed. The amount of change in refractive index with temperature is known as the index-temperature coefficient.
Temperature stabilization has been proposed by using composite dielectric materials as waveguides and/or end mirrors which have little or no net change in index-temperature coefficient. (See, e.g., Z.H.I. Alferov, et al., IEEE Journal of Quantum Electronics, Vol. QE-23, No. 6, 1987). Additional processing required to fabricate such waveguides leads to possible degradation of the laser facets. A copending application of Bradley describes a device for temperature stabilization of diode lasers which does not require deleterious process steps.
Although a group of such lasers with closely spaced temperature stabilized wavelengths would allow a high-density wavelength division multiplexed (WDM) datalink to be implemented, it would be highly desirable to have a single laser module which can emit any of the required channels, preferably via some convenient electronic tuning mechanism. Tunable diode lasers have been demonstrated, but the number of channels that can be utilized is limited by wavelength drift due to temperature induced changes, the same problems that affects DFB and DBR laser stability. This limitation can be overcome by the use of the integrated optic equivalent of a monochrometer. Feedback from a detector at the output of a temperature stabilized monochrometer to the phase control section of a tunable laser would allow tuning of the laser to the desired channel, causing the laser to emit light having the tightly controlled wavelength needed for WDM. It is to this end that the present invention is directed.